Right now the regex is huge and complicated. Imagine trying to prove it captures everything you need, with no lost data, and it captures no more than you need, to maximze the data you can process in available memory. Or imagine you need to hire someone to make changes. You can hire a first year student at X kroner / hour, a second year student at X^2 k/h, a senior at X! k/h .... or even worse, imagine having to figure out next year, what you were had in mind when you programmed it.

If split partitions your problem into smaller, more easily understandable problems, that sounds like a good idea to me. Split is fast and efficient.

Alternately, define a number of small regex, and then assemble them into a larger structure. That way the components are named, so you have an idea what it is intended to achieve, and decipherment is bounded, with a limited number of characters to figure out. Compare to the regex-as-a-whole, where you can't tell where part one ends and part two begins.